Project

LC3 - Limestone Calcined Clay Cement

Goal: LC3 is a new type of cement that is based on a blend of limestone and calcined clay. LC3 can reduce CO2 emissions by up to 30%, is made using limestone and low-grade clays which are available in abundant quantities, is cost effective and does not require capital intensive modifications to existing cement plants.

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Date: 1 April 2013

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Franco Zunino
added a research item
Reducing the carbon footprint of the concrete industry is a priority in the face of global warming. Limestone calcined clay cements (LC 3) provide one of the best options to reduce CO 2 emissions. For optimal implementation, but also to facilitate other low CO 2 solutions, standards that regulate the cement and concrete sector need be adapted quickly. In this article, two main standardisation regions are reviewed in light of the feasibility of adoption and deployment of LC 3 technology. The challenges and limitations are identified, and avenues for further development are proposed.
Franco Zunino
added 2 research items
Synopsis: The adoption of blended cements is the most feasible strategy to achieve a more sustainable industry. In this regard, reducing the clinker factor, while retaining performance, is the key parameter to address. Limestone calcined clays are a promising technology as they offer similar performance to OPC from 7 days onwards, while enabling a reduction of the clinker content of 50%. In some regions of the world like South America, pozzolanic cements (i.e., blended cements that combine clinker with natural pozzolans) have been used for decades. Their clinker factors range from 80 down to 50%. However, their mechanical properties are in general lower as compared to OPC. In this study, we show that by using LC 3-type formulations, cements with the same performance as commercial pozzolanic cements can be produced with clinker contents significantly below 50%. This is explained by the high reactivity of calcined clays and the synergetic reaction of metakaolin and limestone that allows offsetting the clinker reduction.
Synopsis: The optimization of the production process and mixture design using blended cements is an important step to achieve a widespread adoption of these new technologies. In particular, grinding is an important step to ensure good reactivity at early ages and adequate flowability. Grinding aids are normally used to reduce the electrostatic forces between particles and increase the yield of the process. Alkanolamines is a family of molecules that are commonly used for this purpose. In this study, the effect of alkanolamines on LC 3 hydration was studied. It was observed that alkanolamines influence the hydration of the aluminate phases in clinker, particularly ferrite. This leads to an enhanced precipitation of carboaluminates. An increase in early age strength was seen for LC 3 systems incorporating TIPA (triisopropanolamine).
Franco Zunino
added a research item
The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.
Yuvaraj Dhandapani
added 3 research items
This state of the art presents an overview on the effects of calcined clay inclusion on the fresh properties of concrete under the framework of RILEM TC-282 CCL. Progress in recent literature was reviewed to determine the effects of calcined clay, particularly metakaolin and lower grade kaolinite clays, on fresh concrete properties and how to control them using admixtures, particle packing, and mixture proportioning. A summary of recent studies on the use of superplasticizers in modified (or combined form) to improve compatibility have shown promising outcomes to control the rheological properties of calcined clay binders. Superplasticizer demand required to achieve workable concrete increases with increasing dosage of calcined clay and increases substantially for concrete produced with calcined clay at water-to-cementitious material ratios below 0.40. A comparative analysis of data from several literature shows that the addition of calcined clay could reduce setting time when used without superplasticizers. Addition of superplasticizers could help to control and increase the setting time significantly. Calcined clay can be used to make concrete with similar workability and setting times as concrete containing Portland cement through the use of polycarboxylate-based superplasticizers. However, more studies in future should focus on retention of workability by suitable methodologies for various construction activities. Care should be exercised to avoid long setting times with high dosages of superplasticizers.
Conventional use of binary blended cement has been fast changing towards a composite cementitious system which enables the use of two or more substitute materials in conjunction. Limestone and calcined clay cement (LC3) is one such promising blend of composite cement. This ternary combination can significantly improve the substitution level of clinker with good mechanical characteristics. This is owing to the fact that limestone in the presence of calcined clay results in the new chemistry with the formation of additional hydrates. This paper discusses the phase assemblage at different hydration stages in the LC3 cementitious system up to 28 days. The X-ray diffraction technique was used to study the phases in the Ordinary Portland cement, Portland Pozzolana cement and LC3 to understand the phases and their evolution in the different systems. XRD confirmed the formation of carboaluminate phase at an early age. This phase seemed to remain stable up to 28 days. A semi-quantitative estimate suggests an increase in the amount of ettringite (AFt) phase due to stabilization of this phase in the presence of limestone. The amount of bound water was also evaluated for the different hydrated systems. Further, faster depletion of portlandite was observed in the system due to calcined clay’s high reactivity and synergistic hydration kinetics in the LC3 blend.
The use of calcined clay as a substitute material has multiple effects on the evolving microstructure and significantly alters the durability performance of concrete systems. In this study, concretes prepared with calcined clay were characterized for resistance to chloride and moisture ingress using non-steady state chloride migration and unidirectional capillary absorption experiments, respectively. The studies were performed on a range of concrete prepared with a lower grade calcined clay (50% kaolinite content) as supplementary cementitious materials (SCMs) in binary and ternary forms along with fine limestone powder. Notably, the interaction of calcined clay positively influenced physical structure at an early age, i.e., 3 days, which was captured by mercury porosimetry and formation factor assessment. The chloride resistance of concretes prepared with calcined clay significantly improved, and the dilution of hydrates due to limestone addition was effectively neutralized by the synergistic interaction between calcined clay and limestone. Long term moisture ingress was studied using capillary absorption experiments for an exposure period of 28 days, and the results reveal that both binary and ternary binders containing calcined clay had a lower absorption rate than the OPC system. Unlike chloride ingress, the moisture uptake profiles were able to capture the difference caused due to limestone addition explicitly. The transport parameters were examined using estimates of pore network parameter, i.e., formation factor and tortuosity. Concrete prepared with calcined clay and the calcined clay-limestone combination had a higher tortuosity value, which explains improved transport properties using a physicochemical framework. The applicability of these pore network parameters could serve as a basis to conceptualize the link between reactivity, microstructural evolution and transport characteristics in cement composites. Finally, the reactivity of calcined kaolinitic clay is identified as the key factor controlling the early rise in formation factor and improved transport properties in comparison to concrete systems containing conventional SCMs such as fly ashes and slags.
Franco Zunino
added 2 research items
Valorisation of locally available clays for producing blended cements is crucial for a widespread adoption of sustainable binders incorporating these materials. In some places, clays can be intermixed with small amounts of iron sulfides, which could eventually expand in the alkaline media of concrete and lead to cracking if clay particles are sufficiently fine. This study explored the stability of iron sulfides, namely troilite and pyrite, during calcination of clays and their influence in reactivity. It was found that both troilite and pyrite decompose and oxidize into hematite under typical calcination conditions for clays. Furthermore, there is no negative influence of the presence of iron sulfide phases on the reactivity of calcined clays. This shows that these clays are suitable for use in blended cements, provided that adequate quality control is conducted to ensure a complete decomposition of the iron sulfide phases.
LC³ is one of the most promising alternatives for a high-performance blended cement with a significantly lower clinker content and with potential for worldwide adoption. For this reason, understanding its long-term performance is relevant to ensure serviceability over its lifespan. In this paper, a detailed study of phase assemblage, porosity evolution and microstructural development was conducted on LC³ samples hydrated up to 3 years and compared to 90 days specimens. It was observed that the reaction of clinker phases and metakaolin continues between 90 days and 3 years, even after depletion of portlandite. Strätlingite was observed in systems with higher metakaolin contents, in addition to hemi and monocarboaluminate. Experimental results were compared with thermodynamical modelling. New insights are obtained on the hydration mechanisms operating at later ages, when only small pores remain filled with pore solution.
Sripriya Rengaraju
added a research item
Currently, many supplementary cementitious materials are being used along with cement to reduce the CO2 emissions. These cementitious systems exhibit very high resistivity due to pozzolanic reactions and the traditional test methods are inadequate to assess their durability performance related to corrosion, especially chloride threshold (Clth). This paper presents development of a test method (hr-ACT) for determining the Clth of such highly resistive systems with guidelines for identifying the same. The test specimen consisted of a mortar cylinder (lollipop) (cement:sand = 1:2.75) with steel embedded at the centre. Three binders, namely, OPC (w/b = 0.5), PC-FA (70% OPC + 30% Class F Fly ash) (w/b = 0.5) and Limestone Calcined Clay Cement (LC3 - 50% OPC clinker, 31% calcined clay, 15% limestone and 4% gypsum) (w/b = 0.4) and Quenched and Self-tempered (QST) steel were used in this study. The specimens were subjected to chloride in a cyclic wet-dry regime (2 day wet and 5 day dry) and the electrochemical impedance spectroscopy (EIS) test was conducted at the end of each wet period. Statistical analysis was done on the repeated polarization measurements (Rp) to detect corrosion initiation. Once corrosion initiation was detected, the total chloride content (acid soluble chlorides) in the mortar at the Steel Cementitious binder (S-B) interface was determined using SHRP 330 and reported as Clth. The time required to complete hr ACT test for an S B system is about 3-4 months. The Clth was in the order OPC > PC FA > LC3. Also, the synergistic effects of Clth and other parameters on service life are discussed.
Yuvaraj Dhandapani
added a research item
This paper evaluates the suitability of limestone-calcined clay (LC2) combination as a cement substitute material in concrete systems subjected to steam curing. Concrete with blends of Portland cement and LC2 were subjected to short-term heat curing and compared against concrete with plain portland cement and fly ash-based binder (at 30% replacement) for two different concrete systems (a) 400 kg/m3 binder content and 0.40 w/b, and (b) 360 kg/m3 binder content and 0.45 w/b. Several parameters were considered to evaluate the potential of LC2 in such applications, which include - improvements in the 1-day compressive strength, strength gain at later ages, and resistance to chloride-ion penetration. Furthermore, the pore structure, phase assemblage and SEM micrographs were used to assess the alteration in the microstructure at 1-day to elucidate the microstructural development due to steam curing regime. The results show that concrete prepared with LC2 could achieve 1-day compressive strength equal to OPC concrete, which was not achieved with fly ash mixes. The durability performance was similar in both normal and steam-cured concretes across all the binder systems considered in the study. Concrete prepared with LC2 showed significant improvement in 1-day strength due to short-term heat curing. Correspondingly, there was a significant reduction in the porosity and critical pore diameter at 1-day for LC2 systems subjected to steam curing, while fly ash mixes showed almost negligible change in pore structure. LC2 systems could produce a dense microstructure at 1-day, despite the absence of ettringite and carboaluminate phases at elevated curing temperature. The study put forward the beneficial use of LC2 in precast fabrication units with steam-curing requirement for improved early-age strength and durability performance.
Franco Zunino
added a research item
It has been well stablished by several studies that LC3 requires an additional amount of gypsum on top of the normal dosage contained in OPC. In this manner, the second (aluminate) peak do not overlap with the first (alite) peak. This required increase of the sulfate content is attributed to the additional aluminate phases introduced to the system by the addition of calcined clay. However, a correlation between metakaolin (alumininosilicate phase) content and the amount of additional gypsum required for proper sulfation has not been found, and the relationship between these parameters and the position of the aluminate peak is not clear. This study explored in depth this issue in order to further understand the driving mechanism controlling the sulfate demand in LC3. Our results show that there is no direct link between the aluminate phase content and the gypsum demand. On the contrary, the driving mechanism is linked to the specific surface area that the mineral additions (calcined clay and limestone) introduce to the system, interaction commonly referred as filler effect.
Franco Zunino
added 8 research items
A mechanism linking C-S-H precipitations and gypsum depletion Our results show that the ratio of aluminate and gypsum phases cannot explain the kinetics of reaction observed. On the contrary, the overwhelming driving mechanism is linked to the specific surface area that the mineral additions. This additional surface provides nucleation sites for C-S-H precipitation, increasing the rate of reaction of C3S during the acceleration period. As C-S-H adsorbs sulfate, this increase in the precipitation rate leads to an early depletion of sulfate in the pore solution that triggers the second (aluminate) peak. This finding has big implications for a practical implementation of LC 3 and other technologies such as LC 2. The role of the filler effect in sulfate demand of blended cements Phase assemblage and aluminate reaction in OPC and LC 3 In some blended cements, the amount of sulfate required differs from the observed in OPC. This study aimed to understand the mechanism behind the contribution of SCMs to the sulfate balance of blended cements. Our results show that the filler effect associated to the addition of SCMs is responsible for the acceleration and enhancement observed in the aluminate peak. As the rate of precipitation of C-S-H is increased, more sulfate is adsorbed and consequently, the depletion of gypsum is reached earlier during the hydration process. No significant impact of the aluminum content of the SCM was observed, and a relationship between heat release at the maximum of the aluminate peak and the gypsum content of the system was established.
Calcite impurities in clay form a granular deposit on the surface of kaolinite which reduces surface area and slightly impact reactivity. However, the effect is minor and therefore, calcite contaminated clays can be used as SCMs if the content of impurities is in the range explored in this study. The formation of a Ca-bearing glass phase was observed. The presence of gibbsite in raw clays does not interfere with the normal reactivity of the metakaolin available. Therefore, these clays are also suitable for production of metakaolin and use as SCM.
In-situ XRD experiments allowed to study the hydration of LC 3 binders in detail during the first 48 hours. The differences observed between OPC (aluminates from calcined clay and OPC) and C 3 S (aluminates only from calcined clay) phase assemblage allowed to attribute the observed third peak of hydration as the reaction of limestone and aluminates from calcined clay to form CO 3-AFm (synergetic peak). Furthermore, clear evidence of pozzolanic reaction, measured as CH consumption, was found during the first 24 hours of hydration, in good agreement with mechanical and porosity refinement findings of previous studies. Calcined clays provide a promising opportunity to lower clinker levels in cements because of their widespread availability and their excellent reactivity in blended cements. This study explored the interaction between the aluminosilicates from calcined clay and the hydration products of Portland cement, by using in-situ XRD experiments. Samples were prepared using a high shear mixer and placed in a sample holder covered with a Kapton film to prevent evaporation. The results show that pozzolanic reaction occurs significantly already at 24 hours of hydration. In addition, the formation of carboaluminates from the reaction of metakaolin and limestone occurs after the main peak, between 48 and 72 hours of hydration. The experiments performed over C 3 S plus LC 2 (calcined clay limestone blend) allowed to isolate the source of aluminum contributing to different reactions over the first week of hydration. This gives an explanation for the third peak typically observed in isothermal calorimetry experiments of LC 3 binders.
Franco Zunino
added a research item
The climate emergency requires the adoption of strategies and technologies that effectively reduce CO 2 emissions in the short to midterm to keep the global temperature rise below 2°C above pre-industrial levels. Concrete is the substance most consumed by humanity after water. The blended cements in which supplementary cementitious materials replace part of the energy-intensive clinker are the most realistic means to obtain large-scale CO 2 reductions. Limestone calcined clay cements (LC 3)-blended cements produced by the combination of limestone, calcined clays, and portland cement (OPC)-provides a solution that achieves equivalent mechanical performance to OPC, better durability against chloride, and alkali-silica reaction reduction of CO 2 emissions by approximately 40%. Furthermore, it is cost-effective compared to OPC currently on the market. Due to the similarities with OPC, it is a material that can be adopted today using the same construction equipment and workforce worldwide.
Yuvaraj Dhandapani
added a research item
Two-component systems (i.e., Clinker + supplementary cementing material or SCM) compose a major share of cementitious materials in the current scenario. A ternary blended system, with co-substitution of limestone, has the potential to complement the SCMs’ reaction and improve substitution levels of portland clinker. The synergistic interactions between the three components, i.e., clinker-limestone-aluminosilicates, has led to the adoption of finely grounded limestone -aluminosilicate combination as a cement substitute. However, there is a lack of understanding on the complexity brought into such ternary binder systems due to the unique physicochemical contribution of limestone in the hydrating cement matrix, particularly from the viewpoint of describing the physical structure development and its influence on concrete durability parameters. With this background, the current study was proposed to delineate the interaction mechanisms in composite binders by investigating the role of ternary binder systems on binder chemistry, phase assemblage, physical structure development and durability potential of concrete systems.
Yuvaraj Dhandapani
added a research item
The review summarizes literature to examine the transition from portland limestone cement system to composite ternary binder systems involving limestone. Interest in limestone addition as an ideal component in multicomponent binder systems has surged as evident from the large volume of literature published in the recent past. A ternary blended system, with co-substitution of limestone, has the potential to complement the reaction of the supplementary cementitious materials (SCMs). The direct addition of limestone powder helps to attain higher substitution levels of portland cement clinker, improve early age properties, and supplement SCM’s reactivity. However, the dilution of hydrates could hamper the long-term benefits. In this review, the interaction of fine limestone is classified and elaborated under two broad umbrellas: physical and chemical interactions. The physical interactions can manifest in three ways, namely, filler action, shearing action and improved packing, which alters reaction rate and extent at early ages. The chemical interactions also modify the reaction kinetics and phase assemblage due to nucleation of C-S-H on calcite surfaces, preservation of the ettringite phase and formation of carboaluminates. Two different forms of carboaluminate hydrates - hemi-carboaluminate and mono-carboaluminate can be present in the hydrate matrix depending on the balance between carbonate ions and aluminates in the pore solution. Several factors such as replacement level, particle size, choice of SCM, its reactivity and reactive aluminates content, sulphate levels, curing temperature and duration of curing can control the carboaluminate formation, reaction degree of SCMs and chemical interaction from limestone additions. A combination of physical and chemical effects makes fine limestone a potential material for co-substitution with aluminosilicate based SCMs, mainly fly ash, slag and calcined clay. In this review, the factors affecting limestone-SCM composites are summarized based on a detailed literature survey. The effects of SCM-limestone cement composites on hydration kinetics, reaction chemistry, the reactivity of SCMs, the stability of hydrated phases, and contribution to the physical structure development and macroscopic properties by evaluating hydration and mechanical properties are discussed. The importance of AFm (Al2O3–Fe2O3-mono) phases in various deterioration mechanisms in concrete and their influence on performance characteristics in different exposure environment is critically appraised.
Yuvaraj Dhandapani
added 2 research items
A rational understanding of the physical structure development is essential to distinguish the contribution of supplementary cementitious materials (SCM) in a multicomponent cementitious system. Recently, finely grounded limestone is adopted for co-substitution with SCMs due to synergistic interactions between the three components, i.e., clinker-limestone-SCM. However, a clear distinction on the development of the capillary pore space and its link to durability performance such as fluid and ionic transport is challenging to isolate. Ternary binders were prepared with several variants of aluminosilicate based SCMs including three fly ashes, slag and a lower grade calcined clay with a varying dosage of limestone. A physicochemical framework was adopted to examine the durability behaviour of concretes made of ternary binders using formation factor and tortuosity as pore network parameters. The results distinguish a two fold regime to explain the mechanism of physical structure development. Initially, the capillary pores converge to a specific critical size range, i.e., 10-30 nm, and after that, densification occurs due to decrease in pore volume at the critical size range. Further, the paper attempts to explain the densification regime using saturation indices which gives a conceptualise linkage between SCMs' reactivity, pore solution and later age kinetics in composite cements.
When concrete construction is concerned, the most important way to ensure more sustainability is to provide for the desired durability so that material, energy and expenditure is limited for the repair and rehabilitation during the expected service life, in addition to avoiding difficulties caused to the users or inhabitants due to problems that may occur. Therefore, the choice of material through sustainability assessment with durability being an integral part is important. Accordingly, they have been several approaches that have considered durability parameters in the formulation of sustainability indicators. The presentation will review these approaches and use one of them, proposed recently by the authors, to assess concretes with blended binders. The sustainability framework that will be discussed in the presentation mainly considers two indicators, the energy intensity (eics) and the Apathy index (Aichlor), as defined in Table 1. The energy intensity combines the embodied energy or energy consumed in the production of one cubic metre of concrete and the compressive strength that represents the mechanical integrity of the concrete (accounting for structural safety and stiffness). The Apathy index takes into account the carbon footprint and durability, with the latter represented by an appropriate material parameter (FDurability) that influences the service life of a structure made with the assessed concrete; for example, in a structure where durability is governed by the corrosion of steel reinforcement due to chloride ingress, which is a common problem worldwide, this parameter could depend on the chloride diffusion coefficient (Dcl). The sustainability assessment framework aims to facilitate the choice of the concrete composition, among all the options that s that satisfy the usual requirements of strength grade and workability, that yield the lowest energy intensity and the Apathy index.
Franco Zunino
added a research item
Grinding aids are commonly used in cement manufacture to reduce electrostatic forces between powder particles and reduce agglomeration. Alkanolamines are known to also influence the hydration of the aluminate phases in cement. This study assessed the effect of TEA, TIPA and DEIPA addition on the hydration of LC3 systems. It was observed that these molecules have an enhancing effect on the aluminate reaction in LC3. They promote the hydration of ferrite and C3A, and lead to higher amounts of hemicarboaluminate and monocarboaluminate precipitated, which contributes to porosity refinement and mechanical properties. The rate of reaction of metakaolin is not affected by the addition of TEA, independent of the iron content of the clay.
Franco Zunino
added a research item
In limestone calcined clay cements (LC3), more hemicarboaluminate and monocarboaluminate is observed, as compared to other blended cements, from the reaction of metakaolin with limestone. In this study, it is shown that the formation of these carboaluminate phases, predominantly occurs during a “third” hydration peak, after the main alite and aluminate peaks. The influence of the metakaolin content, level of sulfate addition and the water to binder ratio on the position and magnitude of this peak were investigated. This precipitation of hemi and monocarboaluminate has a significant effect on porosity refinement and strength development. It was also observed that alumina from metakaolin can contribute to the precipitation of ettringite if sufficient sulfate is available.
Franco Zunino
added a research item
The combined use of calcined clays and limestone in the ternary system LC3 enables up to 50% of clinker substitution without affecting the performance. Low grade calcined clays are rich in iron. If calcined in an oxygen rich atmosphere, they turn to red. Cement producers avoid selling cement with a color different to the traditional. This paper proposes a method to modify color during calcination by controlling the atmosphere during the cooling. At calcination, the high temperature favors the formation of magnetite even at oxidizing conditions. However, during the cooling phase, magnetite can convert back to hematite if oxygen is available and the calcined material will have a reddish color. The procedure to control color consists of injecting liquid fuel at the carcass of the kiln while the calcined material exits, so that it combusts and exhausts the oxygen available during the cooling process. The procedure was successfully implemented at a pilot kiln in India. Controlling the calcination atmosphere enabled the production of a black calcined clay, instead of a red material. The reactivity and properties of both red and black clay are very similar, and no side effects have impacted properties of LC3 cements produced with the treated clay.
Franco Zunino
added a research item
Limestone calcined clay cements (LC3) are blended cements that combine clinker, limestone, calcined clay and gypsum. The availability of the materials required to produce LC3 and the good performance that it achieves, makes LC3 suitable as a sustainable replacement of Portland cement. Significant advances have been made to assess the properties of LC3, compare it to other common blended cements and establish benchmark characterization procedures. However, there are still open questions that are relevant for a successful adoption of this technology and consequently, to make a better use of the resources available. This research project addresses some of these questions related to processing, blend design and microstructural development of LC3 cements. The effect of calcite impurities in calcined clay reactivity was explored. It was found that at calcination temperatures below the recrystallization threshold, an intermediate produce was formed between kaolinite and calcite. A slight reduction in reactivity was observed, which can be mostly offset by reducing the calcination temperature of the clay and extending the residence time. The effect of using grinding aids was studied at the grinding/classification stage and also during hydration. The use of grinding aids significantly improves the efficiency of dry classification of clay particles, which could prevent overgrinding and increase yield in closed circuit milling units. Furthermore, the use of alkanolamines was shown to be effective to enhance the formation of hemicarboaluminate and monocarboaluminate and thus increase strength. LC3 cements require optimization of the calcium sulfate (gypsum). There is an increase in the sulfate needed relative to the clinker content. The mechanism that explains this increased sulfate demand was found to be linked to the enhancement of alite reaction due to filler effect and the adsorption of sulfate in C-A-S-H, rather than the aluminate content of the calcined clay. In addition, the reaction rate of C3A and the dissolution rate of the sulfate source used are also important to describe the sulfate balance of a cementitious system in general. The effect of hemicarboaluminate and monocarboaluminate on mechanical properties of LC3 was also studied. Metakaolin and sulfate content were found to influence significantly the kinetics of AFm formation. Furthermore, the precipitation of AFm between 2 and 3 days of hydration were directly linked to the strength increase observed. The amount of initial space in the system determines the extent to which hydration takes place at a high rate. Afterwards, the porosity refinement leads to a decrease in reaction rate. However, evidence for a continued reaction of metakaolin in the long term was found. The insights presented in this thesis provide new knowledge that enables a better use of LC3 in the field. Together, they also show the robustness and versatility of this technology, and deliver guidelines for future developments and field implementation of LC3.
Franco Zunino
added 5 research items
Understanding the sulfate balance mechanism of cement is needed for an effective use of sustainable blended cements. Pure phase systems allow to study the interaction between sulfate and each of the phases involved in early age hydration separately. This paper explores the effect of different factors on sulfate requirement in C3S/C3A systems. It was observed that reaction rates of both C3S and C3A have an influence on the overall sulfate balance, as they affect the amount of sulfate adsorbed on C-S-H and the amount of ettringite formed, respectively. Furthermore, the type of sulfate source used (gypsum or hemihydrate) can also significantly change the position of the aluminate peak for the same total sulfate in the system.
Yuvaraj Dhandapani
added 3 research items
In this study, the compositional robustness of limestone-calcined clay combination as clinker replacement in cement, and its effect on concrete performance was assessed in detail. The ratio of limestone-calcined clay in the LC3 with 55% clinker was varied from 1:1.25, 1:2, and 1:3.5 with increasing limestone dosage from 10% to 20%. Additionally, binary binders with calcined clay at 30% (CC30) and 42% (CC42) replacement were studied for benchmarking and dissociating limestone's contribution to the performance of LC3 binder. Concretes were prepared with 360 kg/m 3 and 0.45 with fly ash-limestone and calcined clay-limestone combinations. Early hydration benefits from limestone ensured that binders with a combination of limestone -calcined clay showed higher compressive strength than the binary substitution of 45% calcined clay binder up to 180 days. The higher reactivity of calcined clays resulted in a tremendous rise in resistivity for all calcined clay binders by early curing duration i.e., 7 days. Resistivity development confirmed the synergistic impact of limestone-calcined clay combination , which reaffirms the potential ability of the calcined clay to complement the utilization of higher amount of less energy-intensive limestone in the cementitious materials. Additionally, the influence of varying limestone-calcined clay ratio on time-dependent change in chloride resistance by migration test was probed, and the impact of chloride build-up at the steel surface during service life is also discussed.
In the light of the increasing demand for cement in construction and dwindling reserves of cement-grade limestone, the blend of ground limestone and lower grade calcined clay has emerged as a potential candidate for large volume cement replacement. Studies of such ternary blended systems in paste and concrete reveal very interesting physical and chemical effects on the structure development, strength and durability performance. This paper describes the results of durability studies conducted at IIT Madras on concretes prepared with Limestone Calcined Clay Cement, in comparison with Ordinary Portland Cement and Fly Ash based cement. The focus of the study was to delineate the chemical and physical effects caused by the binder composition on durability indicators for chloride-induced corrosion. The experimental strategy involved the assessment of the pore structure evolution and electrical properties on cementitious pastes, along with measurement of the durability parameters based on moisture absorption, chloride migration and diffusion. The results from the study reveal the complex interplay of the various factors that lead to improved performance of the blended cementitious systems. The synergistic interactions of the blend of calcined clay and limestone impact the physical structure positively at early ages as opposed to fly ash systems, which require prolonged curing to realize their potential.
The present study investigates the effect of concrete mixture proportioning on two major performance parameters which include compressive strength and surface resistivity for limestone calcined clay cement (LC3) and FA30 (70% OPC + 30% Class F fly ash) binders. The findings show that there was a significant early strength development of about 38–88% of the 28th-day strength by 3 days in the range of concrete studied, despite only 50% clinker in LC3 binder. In comparison, FA30 with 70% clinker had about 30–61% of 28th-day strength by 3 days. All LC3 concretes had higher resistivity than FA30 counterparts indicating higher resistance to ionic transport in the binding phase. By 90 days of curing, the surface resistivity values varied between 50–200 and 10–80 kΩ cm for LC3 and FA30 concretes, respectively. Furthermore, a dramatic rise in surface resistivity was seen by 7 days for LC3 concretes conforming to the early impact of calcined clay on the concrete physical structure. In the case of fly ash concretes, resistivity measurements showed a major increase only after 28 days. The pore structure refinement was found to be the significant factor controlling the early development of durability indices in LC3 concretes.
Franco Zunino
added a research item
The use of supplementary cementitious materials as a partial replacement for Portland cement is the most effective way to reduce the carbon footprint of the concrete industry. Raw clays containing kaolinite (kaolin) are promising substitute materials. In the field, raw clays are often mixed with calcite and this is thought to affect their behaviour after calcination. This study explores the influence of calcite impurities on the mineralogy and reactivity a kaolinitic clay. A kaolin sample was blended with different quantities of calcite. The results show that during calcination calcite is decomposed, but no significant amount of free lime or amorphous calcium carbonate are formed. A granular deposit was observed that partially covers the kaolinite particles. The decomposition of calcite and formation of the deposit is associated with a reduction in specific surface area, which increases with the amount of calcite that is intermixed in the raw clay. TEM-EDS analysis showed that the deposit corresponds to a new phase formed from the interaction of kaolinite and calcite, with an Al/Si ratio ranging from 0.74 to 0.88 and Ca/Si ratio between 0.86 and 1.65. Reduction of the calcination temperature to 700 °C reduces the calcite decomposition and the negative impact on reactivity.
Franco Zunino
added a research item
The adoption of blended cements to reduce the carbon footprint has increased significantly over the last decades. Clays containing kaolinite are a promising choice due to their widespread availability. Kaolinite content is the major factor controlling the performance of blended cements incorporating calcined clay, for example in LC 3-50 (50% clinker, 30% calcined clay, 15% limestone and 5% gypsum) clays with a kaolinite above about 40% are needed to achieve similar strength to reference OPCs at 7 days. Materials with low contents of kaolinite are often considered unsuitable. This study compares two fractionation techniques to increase the kaolinite content of a low-grade clay (30% kaolinite content). The results show that kaolinite remains concentrated in the fine particles after grinding. Both wet sedimentation and air separation were effective to increase the reactivity of the material as a combined result of increased fineness and kaolinite content. For the air separation process, it was observed that a significant amount of kaolinite remained in the rejected fraction after processing due to agglomeration of the powder. It was shown that the use of grinding aids before the separation process can further improve the results.
Yuvaraj Dhandapani
added a research item
Numerical simulation of chloride diffusion through high-performance binding systems such as limestone-cal-cined clay cement (LC3) and its comparison to control and fly ash modified concretes is discussed. The simulation framework considers the pore structure of concrete, the concentration-dependence of diffusion coefficient, and Freundlich binding. The LC3 concrete and the companion fly ash concrete exhibit similar service lives (~8× control mixture), despite the LC3 system having a reduced clinker factor than the fly ash concrete (~0.5, as opposed to 0.7). The diffusion model is augmented with a scalar isotropic damage variable that accounts for random distribution of microcracks under fatigue loading (e.g., in a bridge deck). The impact of damage on service life at different stress levels, for the different concretes is elucidated. The modeling approach can be used to evaluate the influence of binder composition and damage on effective service life of chloride-exposed concrete structures, thereby aiding in binder selection.
Yuvaraj Dhandapani
added a research item
This paper presents a summary of the major findings from the studies conducted at IIT Madras on Limestone Calcined Clay Cement (LC3), in comparison with plain portland cement and fly ash-based binder. The study attempts to delineate the chemical and physical effects of binder components in LC3 on hydration and hardening, property development, binder chemistry and durability indicators to evolve fundamental understanding on the performance of such low clinker binders. Such an assessment can drive the practical adoption and extend the applicability of such binders in various domains of cement-based materials. The experimental strategy involved the assessment of the pore structure evolution and electrical properties on cementitious pastes, along with measurement of the durability parameters on concrete for resistance to ingress of moisture by absorption, and chloride ions by migration and diffusion mechanisms. The synergistic interactions of the blend of calcined clay and limestone impact the physical structure positively at early ages as opposed to fly ash systems, which require prolonged curing to realise their potential. The study reveals a combination of calcined clay and limestone can be a potential combination for producing high-performance concrete, more specifically in a chloride laden environment, along with the beneficial alternative resource utilisation and sustainability prospects.
Yuvaraj Dhandapani
added a research item
This paper discusses the role of physical structure alterations on three binder types: plain portland cement, fly ash-based binder and calcined clay-limestone binder. The kinetics of physical structure development and the relevance in transport properties were distinguished using an interlinked parameter in concrete and paste. A systematic experimental investigation was carried out on a range of critical parameters such as strength development, resistivity development, transport characteristics and the time-dependent change in transport parameter. The role of microstructure in terms of the chemical composition of C-A-S-H and its physical states in the different systems is identified as the critical factor governing the development of microstructure. Chloride resistance was assessed by chloride migration experiments for a period of 4 years. The durability behaviours of the concrete with various binder were generalised using pore network parameters such as formation factor and tortuosity. A sensitivity analysis was used to dissect the contribution of the pore solution dilution and pore connectivity to the change in the pore network parameter. Based on the rise in macroscopic physical characteristics (i.e., formation factor here), a two-fold structure development mechanism to conceptualise microstructural evolution in cement composites is presented. Initially, capillary pore space reduces to a critical size range (i.e., 10-30 nm), which is followed by the densification of the physical state of the microstructure. At the point of densification, the pores become largely disconnected which leads to a dramatic increase in the formation factor. The binding matrix in calcined clay concretes reaches the critical pore size at an early age which leads to early densification of capillary pore space region in comparison to fly ash concretes.
Anusha S. Basavaraj
added a research item
The article [Title], written by [AuthorNames], was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 3 December 2018 without open access.
Franco Zunino
added a research item
In some blended cements, the optimum amount of sulfate addition differs from that observed in OPC. This study aims to understand the mechanism behind the impact of two SCMs, namely metakaolin and limestone, on the sulfate balance of blended cements. No significant impact of the aluminum content of these SCMs was observed. Instead, it is observed that the filler effect of the SCM, which accelerates the reaction of alite, is the main factor impacting the sulfate balance. As the rate of precipitation of C-S-H is increased, more sulfate is adsorbed by the C-S-H and consequently, the depletion of gypsum is reached earlier in time during the hydration process. A relationship between heat release at the onset of the aluminate peak and the gypsum content of the system was established.
Anusha S. Basavaraj
added 2 research items
Life cycle assessment (LCA) has been conducted to obtain the potential reduction in the environmental impact due to the production of limestone calcined clay cement (LC3), with respect to ordinary portland cement (OPC) and fly ash based portland pozzolana cement (PPC). A case study of a typical cement cement plant in South India is considered. It is found, for this particular case and the assumptions made, that the CO2 emissions and the energy demand could decrease by 34% and 18%, respectively, if LC3 is used instead of OPC, with the corresponding reductions being 26% and 21% for PPC. A parametric study of some key factors that could influence the impact of LC3 showed that the CO2 emissions and the energy demand could vary by 13% and 20%, respectively, with variations in the calcination energy requirement while the clay transportation distance did not have any significant influence.
The mixture proportioning of concrete for sustainability should consider four aspects, without sacrificing affordability: the lowering of the carbon dioxide emissions; the minimization of raw materials required; reduction of energy demand during manufacturing and construction; and the longevity of the structure or other applications. Taking a set of concretes with different binders, including ordinary portland cement (OPC), fly ash (FA) and ground granulated blast furnace slag (GGBS), sustainability is assessed using different types of indicators including those that take into account the binder and clinker content, compressive strength, carbon footprint and energy demand. A new set of indicators called A-indices has been proposed for combining the influence of carbon dioxide emissions obtained from life cycle assessment (LCA) and durability parameter that relate to the service life of a structure. Here, this concept is illustrated by obtaining a parameter based on the chloride migration coefficient of the concrete. It is proposed that the decision-making process for sustainable concrete be made by minimizing both the A-index and the energy intensity, defined as the energy demand for a unit volume of concrete and unit performance parameter, such as 1 MPa of 1-year compressive strength. The best concretes considered here come out as those with ternary binders having 40% of the OPC replaced by a combination of GGBS and FA.
Yuvaraj Dhandapani
added 2 research items
Various properties of limestone calcined clay cement (LC3) as a binder and those of concretes made with LC3 were assessed during the last four years at IIT Madras to understand its potential as an alternative mainstream cement. LC3 from two major industry-scale productions was used in the evaluation, and the major findings from the research are summarized in this paper. LC3 concretes exhibit compressive strength development comparable to that of concrete made with ordinary portland cement (OPC). In general, they were found to have higher resistance to chloride ingress, moisture ingress, gas permeation, sulphate attack and corrosion-induced cracking, when compared to that of concretes of similar strength grade and/or mixture proportions but having other binders. From the assessment of chloride threshold and carbonation, LC3 concretes were found to have a lower chloride threshold for rebar corrosion and higher carbonation rate than similar strength concretes with OPC and fly ash. However, the service life under chloride attack is expected to be significantly longer for a reinforced concrete structure with LC3 than other commonly used concretes. The ecological impact of LC3 on the cement and concrete production was also found to be positive with a dramatic decrease in carbon footprint when LC3 replaces OPC.
Recent studies on the binder and concrete properties of limestone calcined clay cement (LC3) have shown good potential for producing high-performance, low clinker cement with a combination of limestone and calcined clay [2]. The greater resistance to ionic ingress, more specifically chloride ingress and sulphates, was found to be strongly influenced by the reduced pore sizes due to higher reactivity of calcined clay present in LC3 systems [2]. Even lower grade calcined clay results in an early refinement of pore structure due to highly pozzolanic nature of the amorphous phase [3] and dense microstructure formed in such systems [4]. This alteration in the physical structure is related to the nature and chemistry of hydration products and the variation in the composition of C(A)SH formed in these systems discussed in this paper.
Guillaume Habert
added 2 research items
This study aims to assess alternative materials withstanding low capital investment, with the potential of providing housing affordability for low-income communities. By combining Life Cycle Assessment and Return on Capital Employed techniques, it has been found that glue laminated bamboo housing projects and low carbon cement-based construction materials could foster the scalability of dwelling-places with higher profitability than conventional Ordinary-Portland-Cement-wise investment strategy. The resulting light capital production materials not only can be able to maintain selling prices at an affordable rate, but also will drive more easily the current market for the bottom of the pyramid populations. Through this shift in the material development, the diffusion of appropriate technology implementation on large scale can be more effectively targeted. Finally, these technologies have a lower environmental impact than conventional ones allowing at the same time as a large scale implementation, a potential low carbon path in least developed emerging economies countries.
Africa is currently experiencing rapid population growth and accelerated urbanization. This demographic shift will require a large amount of new construction material resulting in substantial environmental impact. For many cities on the continent, data gaps make specific quantification and robust prediction of this impact highly difficult. This article presents a method to assess the stock dynamics and embodied emissions of a rapidly growing urban built environment using a bottom-up, typological approach. This approach allows for the identification of appropriate engineering solutions for decarbonization by localizing embodied greenhouse gas (GHG) emissions in the different constructive elements with a revisited Sankey diagram. Different alternatives regarding housing type and construction techniques are compared. The city of Johannesburg is used as a case study to illustrate the relation between building types, technologies, and embodied GHG of its residential building stock. This new visualization uncovers the most material- and GHG-intense dwelling types and building elements. The adapted Sankey represents the building stock and its drivers in a simple way, allowing clear understanding of the consequences of potential alternatives. The business-as-usual scenario indicates 100.5 megatons carbon dioxide equivalent (Mt CO2-eq) for new construction between 2011 and 2040. The results of the dynamic model over time show that only a combination of a densified building stock with multistory buildings and the use of alternative construction materials and techniques show real potential to decelerate GHG emissions (33.0 Mt CO2-eq until 2040) while aiming to provide adequate and sustainable housing for all.
Anusha S. Basavaraj
added a research item
The consumption of cement in India and other emerging economies is expected to increase because of the continuing push towards development of housing and infrastructure. The increasing production of cement and utilization of concrete are bound to have a major impact on sustainability. The present work proposes a framework for sustainability assessment, in terms of the CO2 emissions and energy demand, that can be adopted in cases where suitable databases are not readily available. Case studies for cement manufacture have been considered in South India, with different system boundaries such as ground-to-gate, gate-to-gate and CSI. The assessment made using data from the plant and other sources highlights the benefits of using supplementary cementitious materials (SCMs) in terms of reducing the impact of cement and concrete. More importantly, limestone calcined clay cement shows considerable promise in terms of reduction in CO2 emissions and energy demand in both cement and concrete, with more improvement in higher grade concrete.
Yuvaraj Dhandapani
added a research item
This paper presents data on the chloride diffusion coefficient (Dcl), ageing coefficient (m) and chloride threshold (Clth) related to seven concretes (four M35 and three M50) with OPC, OPC+PFA (pulverized fuel ash) and limestone-calcined clay cement (LC3). Using these, the service lives of a typical bridge pier and girder with the PFA and LC3 concretes were found to be much higher than those with OPC concretes of similar strength. From life-cycle assessment, the CO2 footprint of PFA and LC3 concretes were found to be significantly lower than those of OPC concretes of similar strength. Further, the CO2 emissions per unit of concrete per year of estimated service life, as a combined indicator of service life and carbon footprint, are similar for concretes with PFA and LC3, which are much lower than that with OPC.
Anusha S. Basavaraj
added a research item
Anusha S. Basavaraj
added a research item
A framework is proposed, along with two objective indices, for the selection of concrete mixture proportions based on sustainability criteria. The indices combine energy demand and long-term strength as energy intensity, and carbon emissions and durability parameters as A-indices, which represent the apathy toward these essential features of sustainability. The decision support framework is demonstrated by considering a set of 30 concretes with different binders, including ordinary portland cement (OPC), fly ash, slag and limestone calcined clay cement (LC3). In addition to the experimental data on compressive strength, chloride diffusion and carbonation, life cycle assessment has been performed for the concretes considering typical situations in South India. The most sustainable of the concretes studied here, for service life limited by chloride ingress, are those with LC3, OPC replaced by 50% slag, and ternary blends with 20% each of slag and fly ash. In the case of applications where carbonation is critical, the appropriate concretes are those with OPC replaced by 15–30% slag or 15% fly ash, or with ternary blends having 20% slag and 20% Class F fly ash.
François Avet
added a research item
In this study, the C-A-S-H composition, morphology and density are characterized for Limestone Calcined Clay Cement (LC3-50) blends containing clays with various kaolinite contents. Significant incorporation of aluminium is observed for LC3-50 blends compared with reference Portland cement (PC), and this incorporation increases with the kaolinite content of the calcined clay. No change of C-A-S-H morphology was observed by Transmission Electron Microscopy (TEM) between reference PC and LC3-50 blends, with a “fibrillar” morphology for all samples. The determination of the density of C-A-S-H measured by 1H NMR also shows very similar results with a bulk density close to 2.0 g·cm−3 and a solid density of around 2.8 g·cm−3 for all systems.
François Avet
added a research item
The durability of mortar and paste mixtures with respect to chloride ion ingress was investigated for binary blends of Portland Cement Calcined Clay, and ternary systems of Limestone Calcined Clay Cement (LC³). Five clays from various sources with different kaolinite content (17–95%) were studied. The main factor controlling the diffusivity of LC³ systems was found to be the kaolinite content of the clay. Resistance to chloride ingress increased to intermediate levels of kaolinite content and then stabilized. An intermediate kaolinite content of around 50% resulted in two orders of magnitude reduction in diffusivity compared to PC, indicating that the use of high grade (expensive) clays is not necessary to obtain good durability. The chloride binding capacity and distribution of bound chloride between Friedel’s salt and C–A–S–H were quantified for the different systems at fixed water to binder ratio of 0.5. The chloride binding capacity appeared to be a minor factor compared to the porosity refinement in the improved durability of LC³ systems.
Yuvaraj Dhandapani
added a research item
Limestone calcined clay cement (LC3) holds a promising potential to be an alternative low clinker cement in the place of plain portland cement. Over four years of on-going research in India, several properties of LC3 binder and concrete were assessed to understand the potential of LC3 as a mainstream cement. LC3 produced from two major industry-scale productions was used to evaluate a range of properties. The major findings from the research are summarized in this paper. In the different concrete mixes studied, LC3 concretes produce comparable compressive strength development to concrete made with ordinary portland cement (OPC). Concrete made with LC3 was found to have higher resistance to chloride ingress, moisture ingress, gas permeation, sulphate attack (immersion in sodium sulphate solution) and corrosion cracking potential. From the assessment of chloride threshold and carbonation, LC3 was found to have a lower chloride threshold and higher carbonation rate than OPC and FA30. Also, service life estimation limited by chloride attack is expected to increase significantly for a reinforced concrete structure with LC3. The ecological impact of LC3 on the cement and concrete production was also found to be positive with a dramatic decrease in carbon footprint expected if LC3 replaces OPC.
Sundar Rathnarajan
added a research item
Environmental impact due to the emission of carbon dioxide during concrete production can be taken care by reducing the clinker content in the cement. The clinker content can be reduced by replacing it with fly ash and limestone calcined clay. Such systems can have a potential to exhibit enhanced durability/service life when exposed to chloride and carbon dioxide. However, estimating probabilistic service life of concretes with such alternative binder systems is difficult due to the lack of quantitative estimates of the input parameters such as chloride diffusion coefficient (DCl), ageing coefficient (m), carbonation coefficient (KCO2), and chloride threshold (Clth). This paper presents the experimentally observed estimates of these parameters for the following systems: (i) 100% OPC, (ii) 70% OPC + 30% fly ash, and (iii) limestone calcined clay cement (LC3)-known as OPC, PFA, and LC3 concretes, respectively, herein. A total of three concrete mixes were designed. Also, based on these input parameters, the probabilistic service life estimates of a bridge pier and a girder made of these three concretes and exposed to chlorides and carbon dioxide are presented. For chloride ingress study, Fick's 2 nd Law of diffusion and Clth have been used. For carbonation study, a recently developed model for estimating carbonation depth (using mixture proportion) have been used. Then, the life-cycle assessment (LCA) of these three concrete systems in terms of the CO2 emissions per unit of concrete per year of estimated service life is presented-for both chloride and carbonation induced corrosion. In chloride laden environments, the service life of the bridge pier and girder systems could be enhanced by about 10 times by using fly ash or LC3 concretes-for similar strength grade concretes. Also, the average annual CO2 emissions (during the expected service life) of PFA and LC3 concretes could be about 3 and 7 times, respectively, lower than that of OPC concretes of similar strength grade. In case of carbonation-induced corrosion, the limited experimental data indicate that the PFA and LC3 concretes could exhibit a lower service life and higher average annual CO2 emissions (during the expected service life) than OPC concretes.
Sreejith Krishnan
added a research item
The reduction of the clinker factor in cement has emerged as the most promising solution to reduce carbon dioxide(CO2) emissions and to improve sustainability. Limestone calcined clay cement (LC3) is a ternary cement where the synergy between calcined clay and limestone allows the reduction of clinker factors to 0·5. In order to understand practical issues in the production of LC3, such as the selection of raw material and production conditions, industrial production of LC3 has been carried out at three locations in India. A wide range of raw materials was collected from various parts of India and characterised to evaluate their suitability for the production of LC3. Both static and rotary calciners were used for the production of calcined clay. Open- and closed-circuit ball mills were used. Limestones with various impurities and compositions were utilised. It has been observed that lower-grade clay and limestone can be used and that the quality control during the production process can be carried out using widely available techniques. Field trials have shown that the cement can be used without any changes to the existing construction methodologies. This paper discusses the key lessons and insights gained from these trial productions.
Anusha S. Basavaraj
added a research item
Considering that India is the second largest producer and consumer of cement in the world, it is understood that its production and use has a tremendous impact on the energy consumption and carbon dioxide emissions. More than 75% of cement in India is made by blending ground clinker with fly ash, ground granulated blast furnace slag, limestone or other supplementary cementitious materials (SCMs). Further, there have been only limited studies on the sustainability assessment of cement and concrete that can give a clear picture of the impact and help mitigate it in future. The work presented here is based on realistic process maps made in cement plants and data collected from them. The concretes assessed are based on two typical strength grades obtained with blended cements, as well as only portland cement. The results highlight the importance of the SCMs in terms of total energy consumption and carbon dioxide emissions. The study also draws attention to the need to use high grades of concrete to better harness the benefits of the SCMs. Further, the need to generate more relevant data sets for the Indian context is recognized.
Franco Zunino
added a research item
Limestone calcined-clay cements (LC3) take advantage of the synergetic effects of calcium carbonate reaction with the additional aluminium provided by the calcined clay. As temperature decreases, calcium carbonate solubility increase, therefore, the early-age hydration kinetics and the optimal proportioning of the ternary cement system are modified. This study explored the reactivity and mechanical performance of different LC3 systems cured at 10 and 20 ºC. Mixtures containing PC, PC-limestone and a LC3 blends with 50% clinker factors and 2:1 clay-to-limestone ratio were cast and compared. Hydration kinetics were assessed using isothermal calorimetry at each of the temperatures. The evolution of porosity was studied during hydration by MIP. Compressive strength was measured over time on cement paste cubes. Phase assemblage was monitored using XRD.
François Avet
added 3 research items
The present paper introduces a new rapid, relevant and reliable (R3) test to predict the pozzolanic activity of calcined clays with kaolinite contents ranging from 0 to 95%. The test is based on the correlation between the chemical reactivity of calcined clays in a simplified system and the compressive strength of blends in standard mortar. The simplified system consists of calcined clay portlandite and limestone pastes with sulfate and alkali levels adjusted to reproduce the reaction environment of hydrating blended cements. The pastes were hydrated for 6 days at 20 °C or for 1 day at 40 °C. The chemical reactivity of the calcined clay can be obtained first by measurement of the heat release during reaction using isothermal calorimetry and second by bound water determination in a heating step between 110 °C and 400 °C. Very good correlations were found between the mortar compressive strength and both measures of chemical reactivity
This paper presents a comparative study of three methods to determine the amount of reacted metakaolin in calcined clay blends: mass balance, thermodynamic modelling, and the Partial or not Known Crystalline Structure method (PONKCS) based on Rietveld analysis of X-ray diffraction. The methods are applied to Limestone calcined clay cements (LC³-50) in this study. Mass balance and thermodynamic modelling results show good agreement, especially at early age. PONKCS method shows globally comparable results, even if it has higher variability. The precision of PONKCS becomes poor for blends with <60% of metakaolin in calcined clay.
This study presents the influence of the calcined kaolinite content of calcined clays on the hydration of Limestone Calcined Clay Cements containing 50% of clinker (LC³-50). Above a calcined kaolinite content of 65% in calcined clay, further reaction of clinker is inhibited from 3 days onwards. Detail investigation indicates that this slowing down of clinker hydration is related to a significant refinement of pore connectivity. A limiting critical pore entry radius of 3–5 nm is reached, from which the porosity does not get further refined. The higher the calcined kaolinite content, the faster this refinement limit is reached. The formation of carboaluminate hydrates is also limited after reaching this refinement limit. As a consequence, the on-going reaction of metakaolin impacts C-A-S-H, mainly affecting gel porosity, which is not well characterized by MIP.
Jose Fernando Martirena Hernandez
added 15 research items
As part of the validation procedures for low carbon cement (LCC), with only 50% clinker content, its durability performance will be established by exposing specimens and large scale elements to a natural marine environment in the N. coast of Cuba. Before subjecting the elements to the exposure site, it was decided to assess their potential durability by the non-destructive measurement of the coefficient of air-permeability kT (Swiss Standard SIA 262/1:2013) and cover depth. Preliminary trials were run on cast specimens and directly on precast elements industrially produced with mixes of equivalent strength, prepared with the LCC and a conventional OPC. Further, kT measurements were made after the elements have been at the exposure site for almost one year. The kT results are encouraging in terms of the potential durability of LCC concretes and confirm the importance of the quality of the execution on the performance of full scale elements as well as the need of in situ measurements.
This study combines two techniques for the assessment of sustainability in cement and concrete production: Life Cycle Analysis and Eco-efficiency. The first technique is used to assess the environmental impact of Low Carbon Cement (LC3) production from quarrying to the factory´s gate. The LCA is developed in order to compare three Cuban cements and its associated impacts: OPC, PPC and LC 3. For that purpose, an inventory is developed using official statistics of the cement sector, calculated productive and economic indexes and emission factors. Global warming and energy use, are the main identified impacts. The second method is employed for the calculation of the improvement potential derived from the substitution of OPC by LC3 in a model house built with LC3 in Santa Clara city. A considerable improvement of 54 percent in the eco-efficiency indicator has been achieved as a result of using blended cement that is a proper combination of clinker, metakaolin, gypsum and limestone. The results become a challenge for Cuban construction sector in order to generalize the technology as a sustainable product from the economic, social and environmental point of view.
The influence of thermal activation temperature in the pozzolanic reactivity of low grade kaolinitic clay is assessed in this paper. The raw material, with approximately 40% kaolinite and 40% of 2:1 clay minerals, was calcined to temperatures ranging between 500-1000 °C. Mortars with a 30% replacement of OPC by the clay calcined at 800 °C, a temperature representing the best compromise between structural disorder of the clay fraction and its specific surface, show values of compressive strength from seven days on similar or higher than the reference 100% OPC mortars. Pozzolanic reactivity assessed by cumulative heat of lime-pozzolan pastes are in correspondence with these results. The increase in compressive strength with calcination temperature up to 800 °C could be associated to a more complete thermal activation of the multicomponent clay fraction. The experimental results indicate that low grade kaolinitic clay deposits with moderate contents of kaolinite constitute a potential source of high reactivity pozzolanic materials.
Radhakrishna Pillai
added a research item
Chloride induced corrosion is a serious deterioration mechanism in concrete structures. Corrosion rate is an important parameter required to estimate the service life, especially propagation life, of concrete structures. The corrosion rate of the embedded steel significantly depends on the properties of the surrounding concrete and cementitious systems. The thermo-mechanically-treated (TMT) steel is widely used in Indian construction. However, literature provides very limited information on corrosion rates of TMT steel embedded in concrete with Ordinary Portland Cement (OPC) and Limestone Calcined Clay Cement (LC3). This makes it difficult to quantify and compare the service life of such systems. This paper presents experimental results on the corrosion rates of TMT steel embedded in mortar (w/c = 0.5) with OPC and LC3. Each test specimen (lollipop type) consisted of an 8 mm diameter steel rod embedded in a 100 mm long mortar cylinder with a 10 mm cover. To accelerate the corrosion studies, chlorides were premixed to the mixing water/mortar. Four levels of premixed chloride content (i.e., 0, 3, 6, and 9 % NaCl) were used. A total of 40 lollipop specimens with 5 replicas for each variable combination were prepared. Corrosion rates were measured using Linear Polarization Resistance (LPR) technique and were monitored for a period of 2 months. Comparison of the corrosion rates and propagation periods for the steel embedded in systems with OPC and LC3 are presented.
Yuvaraj Dhandapani
added 2 research items
Conventional use of binary blended cement has been fast changing towards a composite cementitious system which enables the use of two or more substitute materials in conjunction. Limestone and calcined clay cement (LC³) is one such promising blend of composite cement. This ternary combination can significantly improve the substitution level of clinker with good mechanical characteristics. This is owing to the fact that limestone in the presence of calcined clay results in the new chemistry with the formation of additional hydrates. This paper discusses the phase assemblage at different hydration stages in the LC³ cementitious system up to 28 days. The X-ray diffraction technique was used to study the phases in the Ordinary Portland cement, Portland Pozzolana cement and LC³ to understand the phases and their evolution in the different systems. XRD confirmed the formation of a carboaluminate phase at an early age. This phase seemed to remain stable up to 28 days. A semi-quantitative estimate suggests an increase in the amount of ettringite (AFt) phase due to stabilization of this phase in the presence of limestone. The amount of bound water was also evaluated for the different hydrated systems. Further, faster depletion of portlandite was observed in the system due to calcined clay's high reactivity and synergistic hydration kinetics in the LC³ blend.
The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.
Anusha S. Basavaraj
added a research item
This poster highlights the important parameters, which influences the environmental impact of different types of Cements in India.
Aurélie Favier
added 2 research items
Supplementary materials that are utilized to replace ordinary Portland cement (OPC) decrease the workability of the cementitious mixtures and superplasticizers are usually added to cement to control their fluidity. In general, current superplasticizers are solely optimized for single component systems such as OPC. Here, we report the performance of a series of a modified poly(carboxylate ether)-based superplasticizers (PCEs) in a ternary OPC-calcined clay-limestone blend. We have utilized: i) a co-monomer with high ionic character, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) to be incorporated into the acrylic acid backbone of PCEs and ii) low density of polyethylene glycol (PEG) grafted chains < 0.01 mol/mol. The optimized polymer does not inter-calate into the layered structure of calcined clay and preserves its steric size in the presence of high concentration of sulfate ions.
This volume focuses on research and practical issues linked to Calcined Clays for Sustainable Concrete. The main topics are geology of clays, hydration and performance of blended system with calcined clays, alkali activated binders, applications in concrete and mortar, durability of concrete under various aggressive conditions, and economic and environmental impacts of the use of calcined clays in cement based materials. This book compiles the different contributions of the 2nd International Conference on Calcined Clays for Sustainable Concrete, which took place in La Habana, December 5th-7th, 2017.The papers update the latest research in their field, carried out since the last conference in 2015. Overall it gives a broad view of research on calcined clays and their application in the field of construction, which will stimulate further research into calcined clays for sustainable concrete.